I know this is a slightly older topic, but I came across it just now and thought it was interesting.
In regards to whether or not Brian sang on Lady Lynda, I found this video on Youtube recently:
http://www.youtube.com/watch?v=Lm0rdP8cf6c . Ron Altbach commented on it:
"I co-wrote this with Al. We wrote it in Big Sur in 1976 The only BBoys on the vocals are Al and Mike. Bobby Figueroa, Eddie Carter, Eddie Tuleja and I were the back-up vocals. The electric wurlitzer piano was originally the sound my band King Harvest used on Dancing in the Moonlight. So, yes, this was in the same kind of non-bboys production that Al and I did on MIU. And we had a great time doing it. Ron Altbach"
I would assume he's talking about the released version on L.A., but he may be referring to the alternate version in the video. Either way, it's highly unlikely Brian sang on it at all.